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Compound V2 is the original implementation of the Compound algorithmic interest rate protocol that defined the money-market template most of DeFi later copied. Suppliers deposit assets and receive cTokens that accrue interest; borrowers post any combination of collateral assets and borrow against the shared pool.
V2 has been largely superseded by V3 for new activity but remains live with substantial outstanding deposits and is governed by the same COMP holders through Compound Governance.